Rhizobial ecology of the woody legumePsorothamnus spinosus in a Sonoran Desert Arroyo

Abstract

Psorothamnus spinosus seedlings were selected at random and excavated from 10 • 30 m quadrats along a 270 m transect in a southern Californian desert arroyo. Forty-six of the fifty seedlings excavated (92%) were nodulated. The mean number of nodules/plant was 7.0 ___ 3.6. Maximum rooting depth was 40 cm, and most (58.8%) of the nodules were found between 15 and 30cm depth. The mean root/shoot ratio was 1.4 _+ 0.4. The rhizobial population density between 10 to 40cm depth across all quadrats was non-detectable using a plant infection, most probable number method. All 70 isolates from field nodules were fast-growing Rhizobium spp. Two colony morphologies were observed: wet, translucent, and wet, opaque. All isolates tested were effective on both P. spinosus and another desert woody legume, mesquite (Prosopis glandulosa). Many isolates had a high relative efficiency, and seven of eight efficient isolates had uptakehydrogenase activity. Root stimulation of the low rhizobial population found in the arroyo and subsequent root nodulation may be an important factor in seedling establishment by woody legumes in N-limited desert arroyo systems.

Rhizobia associated with neotropical tree Centrolobium tomentosum used in riparian restoration

“…Like other tropical legume trees as Prosopis (Jenkins et al 1987), Acacia (Odee et al 2002), and Albizia spp. (Wang et al 2006), C. tomentosum is nodulated by fast-and slow-growing strains.…”

“…They confirmed that the legume species within the genera Acacia, Albizia and L. leucocephala may harbor some common rhizobial species, but they also have different preferences of the microsymbionts. Jenkins et al (1987) showed that the surface and phreatic soil environments selected for different rhizobial characteristics in another woody legume Prosopis glandulosa, since the low-nutrient phreatic zone with greater constancy in water content and temperature than the surface soil favors SG isolates. In contrast, Dupuy and Dreyfus (1992) reported SG rhizobia in surface and deep soil isolates from Acacia albida.…”

“…In contrast, Dupuy and Dreyfus (1992) reported SG rhizobia in surface and deep soil isolates from Acacia albida. Heal and Ineson (1984) On the other hand, the surface environment (more heterogeneous or patchy environment with spatial and temporal variation in soil nutrient availability, water content, population density and activity of the other soil biota) should support both SG and FG organisms, although FG are predicted to have the advantage of being favored in conditions of climate adversity and a diversity of microsites capable of supporting SG as well as FG strains may be available in the surface rooting zone (Jenkins et al 1987). In this study, fast growing isolates were dominant in revegetated site and nursery seedlings (disturbing soils) reinforcing this hypothesis.…”

Diversity of Rhizobium Bacteria Isolated from the Root Nodules of Leguminous Trees

“…Dommergues et al (8) summarized recent findings and proposed that nitrogen-fixing trees could be divided into the following three broad groups according to their nodulation patterns with fast-and slow-growing tree rhizobia: group 1, which forms nodules with fast-growing strains; group 2, which forms nodules with both fast-and slow-growing strains; and group 3, which forms nodules with slow-growing strains. Accordingly, we propose that Acacia senegal, Prosopis chilensis, and Leucaena leucocephala belong to group 1, since they were nodulated only by fast-growing tree rhizobia ( (19). Thus, Prosopis glandulosa belongs to group 2.…”

Microbial Symbionts of Plants

“…However, these legume species require droughttolerant rhizobia to form effective symbiosis under arid climates. Rhizobia with survival ability, which showed effective symbiotic characteristics with their host legumes (e.g., Prosopis rhizobia) in desert soils and arid regions, were identifi ed (Jenkins et al 1987 ). Athar and Johnson ( 1996 ) reported that two mutant strains of R. meliloti were competitive with naturalized alfalfa rhizobia and were symbiotically effective under drought stress.…”